This invention relates generally to a mechanism for suppressing capstan driving motor noise and vibration on a videotape deck. Particularly, the invention relates to an art for preventing switching noise, caused by a switching control (e.g., a pulse width modulation (PWM) control) of a direct driving motor current in which a motor shaft is directly coupled to a capstan axis, from affecting images.
Conventionally, as to a capstan driving motor for a videotape deck, a method of full-wave or half-wave current linear driving is generally adopted. However, in order to achieve power-saving, high resistance to voltage, speed-up and suppression of heating, rather than this kind of the driving motor, it has been known to use a direct driving motor [an] output shaft of which can be directly connected to a capstan axis, and which is controlled by PWM the method. As disclosed in a publication of unexamined Japanese Utility Model Application No. 59-117284, said direct driving motor controlled by the PWM method is structured by a rotatable rotor provided with a 9 ring-shaped magnet, and a stator core facing to the magnet of said rotor and having a driving coil. Although this shows a brushless motor facing to a surface of the magnet, this structure can also be applied to a brushless motor facing to a periphery of the magnet.
However, the above-mentioned PWM direct driving motor gives the driving coil higher voltage than the motor of the linear driving method does, and intermits (perform switching to) its current, as shown in FIG. 7, so that harmonics elements generate in a rising edge and a falling edge of the rectangular current. The harmonics elements become large switching noise, and the current containing the noise is induced on the stator core. In this state, since the motor is mounted on a deck chassis as an electrically conducting material in a conducting state, the current containing the noise is propagated to the deck chassis, and then, it is propagated through the deck chassis to the cylinder drum having a head, then further propagated to a video circuit and an audio circuit. Thus, the switching noise, which also contains frequency elements of a video band and a sound band, causes video screen noise (jitter) or audio noise. That is, the PWM direct driving motor gives the high frequency noise to the head amplifier and the like, which makes an unbearable state for watching and listening.
This invention is made to solve the above-mentioned problems. The first object of the present invention is to provide a mechanism for avoiding propagation of driving motor noise and vibration on a tape deck, which, by using a direct driving motor controlled by the PWM method for driving a capstan, prevents switching noise of said motor from propagating to a cylinder head drum, a video circuit and an audio circuit, thereby suppressing the video screen noise and audio noise.
Further, when the direct driving motor controlled by PWM method is mounted on the deck chassis by using an insulating material such as resin in order to suppress said noise, the vibration of the motor may be propagated to the deck chassis, which causes vibration resonant sound, or increases screen jitter. The second object of the present invention is to provide a mechanism for preventing propagation of driving motor noise and vibration on a tape deck, which can resolve the problem caused by said vibration.
In order to achieve the above-mentioned objects, according to one aspect of the present invention, a mechanism for preventing propagation of driving motor noise on a tape deck comprises a deck chassis, a pinch roller and a capstan axis for conveying a tape, a motor which is mounted on said deck chassis for driving said capstan axis, and a cylinder drum which is mounted on said deck chassis and provided with a head for magnetic-recording and playing for the tape: wherein said motor is a direct driving motor in which a motor shaft is directly coupled to the capstan axis, and which is controlled by switching; and, wherein said motor is electrically insulated from said deck chassis.
In the above-mentioned constitution, when the direct driving motor is controlled by switching, current of comparatively high voltage is intermitted, so that switching noise containing harmonics elements generates in the stator core of said motor. However, the motor and deck chassis are electrically insulated from each other, which prevents the switching noise from propagating to the deck chassis, and further avoids it from propagating to the cylinder drum, a video circuit and an audio circuit. Therefore, this constitution makes it possible to suppress video screen noise and audio noise.
In the above-mentioned constitution, the direct driving motor is mounted on the deck chassis through an insulator.
Further, in the above-mentioned constitution, said direct driving motor comprises a rotational axis as a capstan axis, a rotor which is mounted on said rotational axis, a stator core which is wound by a coil being supplied PWM control current and faces to said rotor, and a bearing holder which holds said stator core and supports said rotational axis, and said direct driving motor is mounted through said bearing holder on the deck chassis, wherein said bearing holder is made of an insulating material. If resin is used as the bearing holder, for example, this constitution prevents the switching noise from propagating to the deck chassis in a comparatively simple structure.
In the above-mentioned constitution, said cylinder drum can be mounted on the deck chassis through an insulator.
According to another aspect of the present invention, a mechanism for preventing propagation of driving motor noise on a tape deck comprising a deck chassis, a pinch roller and a capstan axis for conveying a tape, a motor which is mounted on said deck chassis for driving said capstan axis, and a cylinder drum which is mounted on said deck chassis and provided with a head for magnetic-recording and playing for the tape: wherein said motor is a direct driving motor in which a motor shaft is directly coupled to the capstan axis, and which is controlled by switching; and, wherein said motor comprises a rotational axis as a capstan axis, a rotor which is mounted in said rotational axis, a stator core which is wound by a coil being supplied switching control current and faces to said rotor, a bearing holder which is made of an insulating material for holding said stator core and supporting said rotational axis, and a motor PCB (printed circuit board) which is supported by said bearing holder and on which circuit elements for controlling the motor are mounted, and wherein said motor is secured on the deck chassis through the bearing holder; and, wherein said motor PCB is held in close to where the bearing holder is mounted on the deck chassis, and supported by a supporting member in an electrically insulating state at a distance from where the motor PCB is held.
In the above-mentioned constitution, the direct driving motor controlled by a switching control is mounted on the deck chassis by using the bearing holder made of an insulating material such as resin. Although vibration caused by a decrease in mechanical securing strength of said motor in an activation thereof may propagate to the deck chassis, the motor PCB is held by the bearing holder, and besides, supported by the supporting member in the electrically insulating state from the deck chassis. Accordingly, this constitution prevents generation of vibration resonant sound and increase of screen jitter.
In the above-mentioned constitution, the supporting member can be composed of a boss made of resin which is provided extending toward the motor PCB on the deck chassis. Further, the supporting member can be an extending part of an insulating holder for holding members mounted on the deck chassis. Furthermore, the supporting member can be composed of a projection formed on the deck chassis, and an insulating material intervened between said projection and the motor PCB.